PB2372: PP2A INHIBITOR LB100 ENHANCES THE SENSITIVITY OF NPM-ALK+ALCL TO CRIZOTINIB AND REVERSES THE RESISTANCE OF ALCL TO CRIZOTINIB
Authors: Wenyu Shi
Journal: HemaSphere (2023)

Topic: 20. Lymphoma Biology & Translational Research Background: Anaplastic large cell lymphoma (ALCL) is a rare and aggressive non-Hodgkin’s lymphoma that is commonly diagnosed in children and adolescents. Although conventional chemotherapy based on conventional CHOP (cyclophosphamide, adriamycin, vincristine, prednisone) achieves high remission rates in ALCL. However, relapse and drug resistance occur in more than 40% of patients. The clinical use of the ALK inhibitor crizotinib on most relapsed refractory NPM-ALK+ALCL has demonstrated robust and effective treatment in recent years, but crizotinib resistance still occurs in 30% of cases. This urgently requires us to find new treatments to enhance the sensitivity of crizotinib as well as to overcome the resistance of crizotinib. Aims: The purpose of this study is to investigate whether the PP2A inhibitor LB100 could enhance the sensitivity of NPM-ALK+ALCL to crizotinib and reverse its resistance. Methods: In this study, we applied PP2A inhibitor LB100 in combination with crizotinib to normal ALCL cell lines and explored the altered biological activity by CCK8, clone formation, EdU. We used flow cytometry to detect the changes in apoptosis and cell cycle and then applied Western blot and immunofluorescence to verify the mechanism of cell cycle alteration. At the same time, we used PCR, Western blot, and lipid ROS assay to verify the specific mechanism of action of the two drugs leading to iron death in cells. Further, A crizotinib-resistant strain was constructed, and the effect of reversing resistance was observed by acting a single LB100 and two drugs separately on the resistant strain. Results: The PP2A inhibitor LB100 was found to significantly inhibit the viability of normal and drug-resistant ALCL cell lines and to be more sensitive in drug-resistant lines. LB100 significantly enhanced the killing effect of crizotinib in normal tumor cell lines and partially reversed crizotinib resistance in resistant lines. Western blot and immunofluorescence experiments showed that LB100 leads to increased cellular G1 phase block by increasing cellular DNA damage, which in turn enhances the sensitivity of crizotinib. At the same time, PCR and Western blot showed that the downregulation of cholesterol mevalonate pathway-related molecules and GPX4, a key molecule for iron death, accompanied by upregulation of lipid ROS, occurred after the combined effect of the two drugs. It was suggested that LB100 may also exert a sensitizing effect by inhibiting the mevalonate pathway, leading to iron death of cells. Summary/Conclusion: In conclusion, LB100, as an effective inhibitor of PP2A, can significantly increase the effect of crizotinib against normal NPM-ALK+ ALCL, inhibit the growth of crizotinib-resistant strains, and partially restore the sensitivity of crizotinib, which could be a new therapeutic tool for ALCL. Furthermore, simultaneous targeting of PP2A and ALK has a high potential in overcoming ALK inhibitor resistance in ALCL and could be a new therapeutic strategy to overcome drug resistance. Keywords: T cell lymphoma